Research in our laboratory has focused on plasma lipoprotein and apolipoprotein (apo) composition and metabolism in normal and dyslipoproteinemic subjects. ApoA-I and apoA-II, the major protein constituents of human high density lipoproteins (HDL), have been extensively studied in terms of their site of production, plasma kinetics, and their relationship to various disease states. In addition a patient with an absence of apoA-I, a marked reduction in HDL, and premature coronary heart disease, has been identified, representing the discovery of a new disease entity. The interaction of apoA-I and apoA-II with plasma lipases is also being investigated. Ongoing studies of apoE metabolism support the concept that most patients with type III hyperlipoproteinemia (HLP) have an abnormal apoE. In addition, a patient with type III HLP associated with an absence of apoE has recently been found, and represents a new cause for this form of HLP. The effects of various diets on plasma lipoproteins and apolipoproteins are continuing projects under investigation.